The overall goal of our work is to cure Huntington's Disease (HD). This proposal seeks to evaluate new intracellular antibodies (intrabodies) directed against the Huntingtin (htt) protein using an established Drosophila model for HD. Work in tissue culture cells and brain slice preparations has demonstrated that intrabodies can ameliorate pathology associated with expression of mutant forms of the htt. We have recently demonstrated that our prototypical anti-htt intrabody, C4 scFv, partially suppresses HD pathology in the functioning nervous system of Drosophila. The degree of suppression is quantifiable, allowing the rapid evaluation of new intrabodies for improved efficacy over our existing intrabody. Additionally, through unbiased functional genetic screens available in Drosophila, the cellular processes triggered by the intrabody/target interaction that result in disease correction can be elucidated. Identification of cellular pathways involved in intrabody-dependent correction of pathology will allow us to devise strategies to augment intrabody therapy as well as predict potential deleterious side effects. Finally, we will develop new models for testing intrabodies in flies. Currently, the intrabody and disease-causing htt transgene are co-expressed from early embryonic stages onward. In humans, therapy with intrabodies would likely commence in adults after the onset of diseases. Our new model will allow testing of intrabody efficacy at any time subsequent to the onset of disease. If successful this will provide validation of intrabodies as disease therapeutics and impetus to proceed to preclinical testing in vertebrate models of HD.